Twitter owner Elon Musk has launched a new logo – the single letter "X" – to replace the social media service's famous blue bird.
The X design started appearing at the top of Twitter's computer version on Monday.
But the old bird logo could still be seen across areas of the service.
Musk announced in a Twitter message Sunday that he had decided to change the company's logo.
He said he had asked his millions of followers to provide logo ideas and if they would favor a change in the service's colors from blue to black.
When asked what tweets would be called without the blue bird logo, Musk said they would now be known as "Xs."
The latest change is one in a series Musk has carried out since buying Twitter for $44 billion last year.
The billionaire businessman dismissed about 75 percent of the company's workforce soon after the deal closed.
Musk said the move was necessary to make Twitter more effective and increase profits.
He also announced plans to start charging Twitter users eight dollars a month to keep a verified account.
As Twitter chief, Musk also lifted some existing restrictions on user content.
He said those changes were part of a larger effort to protect the free speech of Twitter users.
Critics said his plans were likely to increase the amount of harmful content and hate speech appearing on the service.
Musk's changes led to drops in the number of Twitter users.
Some advertisers stopped doing business with the company, as well.
In a message on Twitter Monday, chief executive Linda Yaccarino wrote, "X is here! Let's do this."
Along with her message, she published a picture of the logo projected onto the building's headquarters in San Francisco
Musk also commented on the logo change, writing, "And soon we shall bid adieu to the twitter brand and, gradually, all the birds."
Musk said the X.com web domain was already redirecting users to Twitter.com.
A three-member team designed the first Twitter logo in 2012.
One of those designers, Martin Grasser, described the blue bird logo as "simple, balanced" and easy to read at very small sizes.
Matt Rhodes is with the British creative agency House 337.
He told news agency Reuters that making changes to such an established brand presents big business risks.
"Anything that makes it harder for people to find, or want to open the app on their cluttered phone screens risks harming usage," Rhodes said.
However, Paolo Pescatore, a technology and media specialist who founded advisory company PP Foresight, said the change could be good.
He spoke to the Associated Press.
Pescatore said social media users currently can get confused by too many apps and messaging services to choose from.
Driving users to one central place will "engage" more users and could make Twitter easier to use, he said.
Musk has long been interested in the letter X.
He had already changed Twitter's official name to X Corp after buying the company.
The billionaire is also CEO of rocket company Space Exploration Technologies Corporation, commonly known as SpaceX.
He started an artificial intelligence company this month called xAI to compete with OpenAI.
And in 1999, he founded a startup called X.com, an online financial services company now known as PayPal.
Musk's Twitter purchase and rebranding effort are seen as steps toward his stated plans to create what he has called an "everything app."
Such an app would be similar to China's WeChat, which combines video, messaging, streaming and payments.
Yaccarino wrote on Twitter that she sees X becoming "the future state of unlimited interactivity – centered in audio, video, messaging, payments/banking – creating a global marketplace for ideas, goods, services, and opportunities."
I'm Bryan Lynn.